A puzzle game is a well-known amusement device that tests the ingenuity and patience of the player. With commonplace puzzle games, the player is required to correctly fit together a collection of small planar pieces. Each piece has an image-bearing surface constituting an individual pictorial entity. When the various pieces of the puzzle are correctly combined, the pictorial entities visually unite to form a large complete image. These types of puzzle games have a bi-dimensional character because all the pieces are interlocked in a co-planar relationship and the resulting assemblage is flat.
To increase the satisfaction and pleasure derived from a puzzle game, toy manufacturers have developed in the past recent years puzzle games providing a three-dimensional pictorial representation of a building-like structure. Such puzzle games include wall pieces that are interlocked in a planar configuration through dovetail joints to form the walls of the building. The walls are joined to one another at the corners of the building by straight tenon and mortise joints that allow the wall pieces on either side of a corner to be united at right angle. The building walls are erected and stand on a /horizontal base that is assembled from a plurality of interlocked base pieces.
The pieces of three-dimensional puzzle games are usually manufactured from polymeric foam backing having the density and thickness dimension required for bearing the weight of the building-like structure. The foam backing is laminated with lithographic film providing each puzzle piece with an image-bearing surface.
A critical element of a three-dimensional puzzle game is the ability of the planar pieces to unite at in a non-planar configuration to form corners. Prior art designs rely on the frictional engagement between a straight tenon and a conforming mortise to interlock the pieces into a corner configuration and prevent unwanted separation that may cause the erected puzzle structure to collapse. When the puzzle pieces are fresh the dimensional tolerances are close to nominal values which makes possible to attain a comparatively tight fit at the corner joints. Accordingly, the level of frictional engagement tenon/mortise is high enough to prevent unintended corner joints separation. However, over time, the fit tenon/mortise may loosen as a result of successive assembly/disassembly of the puzzle parts, or changes in the polymeric foam due to aging. Consequently, the puzzle structure is no longer structurally sound and may partially or totally collapse when subjected a small accidental impact.